In a fan feeding air by rotation of impeller, dust in the air may touch and attach to blades of the impeller. In particular, a sirocco fan has a narrow space between blades, and thus attachment and accumulation of dust result in degradation of its performance.
(Prior Art 1)
To solve this disadvantage, an adsorption net is provided ahead of airflow of the impeller in a centrifugal fan built in a spinning machine to reduce dust touching the impeller. The impeller is periodically rotated backwards to remove dust. (For example, see PTL1.)
The centrifugal fan in PTL 1 is described below with reference to FIG. 7, which is a side view of a conventional centrifugal fan built in a spinning machine.
As shown in FIG. 7, adsorption net 103 is disposed at the side of intake airflow 102 of duct 101. Air outlet 106 is formed at the blowing side of guide plate 105 covering impeller 104 inside duct 101. When impeller 104 is operated in positive rotation direction 107, adsorption net 103 removes coarse dust 108. However, fine dust 109 that cannot be removed by adsorption net 103 accumulates on impeller 104. After fine dust 109 accumulates up to a predetermined level, impeller 104 is operated in inverse rotation direction 110. As a result, airflow colliding with blade 111 changes, and accumulated fine dust 109 comes off.
(Prior Art 2)
In a centrifugal fan built in a range hood, the rotation speed of the impeller is increased for a predetermined time after the normal operation, so as to remove accumulated oil. (For example, see PTL2.)
The centrifugal fan in PTL2 is described below with reference to FIG. 8 that is a side view of a conventional centrifugal fan built in a range hood.
As shown in FIG. 8, purifier 203 is provided on intake passage 202 of hood housing 201. Vent 206 is formed on the blowing side of fan case 205 covering impeller 204 inside hood housing 201. When impeller 204 is under normal operation, purifier 203 partially removes oil 207 drawn in from intake passage 202. A portion of oil 208 not removed by purifier 203 accumulates on impeller 204. After the normal operation that causes accumulation of oil 208 on impeller 204, the rotation speed of impeller 204 is increased for a predetermined time. As a result, the speed of airflow colliding with blades 209 of impeller 204 increases, and thus accumulated oil 208 comes off.
(Prior Art 3)
In a centrifugal fan built in a ceiling of a rail car, a rotary brush slidably blows air to the impeller. (For example, see PTL3.)
The centrifugal fan in PTL3 is described below with reference to FIG. 9 that is a side view of a conventional centrifugal fan built in a ceiling of a rail car.
As shown in FIG. 9, impeller 302 is disposed in wind-direction flap 301. Rotary brush 303 rotates and slidably contacts impeller 302 via an opening in a part of wind-direction flap 301. In addition, air 305 from air nozzle 304 collides with impeller 302 via the opening in a part of wind-direction flap 301. The operation of impeller 302 is stopped for cleaning, and rotary brush 303 and air 305 remove dust 306 accumulated during the normal operation of impeller 302.
However, in the aforementioned centrifugal fans, dust naturally accumulates more easily on the impeller if the centrifugal fan is operated under dusty environment. Rotation of impeller to which dust is attached becomes imbalanced, resulting in damage to the impeller. Therefore, the operation in inverse rotation, operation at increased rotation speed, or cleaning operation is frequently executed for maintenance.